The present invention relates to a method of and an apparatus for forming an interconnection, and more particularly to a method of and an apparatus for forming a fine interconnection in a highly integrated circuit formed on a semiconductor substrate such as a semiconductor wafer or the like.
Aluminum or aluminum alloy has generally been used as a material for forming interconnection circuits on semiconductor substrates. It has been customary to grow a film of the material according to a process such as sputtering, CVD, or the like and then produce a pattern in the film according to etching or the like. As the level of circuit integration increases in recent years, there is a demand for the usage of silver, copper or its alloy, which has a higher conductivity, as an interconnection material. Since it is difficult to etch these materials, it has been proposed to immerse a substrate having interconnection pattern trenches therein in a plating liquid and perform electrolytic or electroless plating on the substrate to embed the trenches with silver, copper or its alloy.
However, while the plating processes are an inexpensive and highly technically accomplished technology, the electrolytic plating process is capable of growing a film only on an electrically conductive material, whereas the electroless plating process suffers a problem in that substances contained in the plating liquid affect the natural environment and the working environment. Accordingly, there has been a strong need for the development of a metal interconnection technology as a substitute for the plating processes.
The present invention has been made in view of the foregoing problems and demand. It is an object of the present invention to provide a method of and an apparatus for forming an interconnection by stably depositing an interconnection metal of good quality as a substitute for the conventional plating processes.
According to an invention described in claim 1, there is provided a method of forming an interconnection, comprising the steps of preparing a substrate having fine recesses formed in a surface thereof, dispersing ultrafine particles made at least partly of a metal in a predetermined solvent, producing an ultrafine particle dispersed liquid, supplying the ultrafine particle dispersed liquid to the fine recesses of the substrate, heating the substrate to melt and bond the metal, and chemical mechanical polishing the surface of the substrate to remove an excessively attached metal therefrom.
With the above arrangement, it is possible to easily form interconnections according to so-called single and dual damascene processes.
The ultrafine particle dispersed liquid may be placed in a container, providing a liquid reservoir, and the substrate may be immersed in the liquid reservoir to supply the ultrafine particle dispersed liquid to only the fine recesses of the substrate. Alternatively, the ultrafine particle dispersed liquid may be supplied to the fine recesses of the substrate by being coated or sprayed in the fine recesses of the substrate and/or on areas surrounding the fine recesses. Furthermore, the ultrafine particle dispersed liquid may be coated by a spin coating process.
According to an invention described in claim 2, the method according to claim 1 comprises the step of evaporating the solvent between the step of supplying the ultrafine particle dispersed liquid to the fine recesses of the substrate and the step of heating the substrate to melt and bond the metal.
According to an invention described in claim 3, in the method according to claim 1 or 2, each of the ultrafine particles comprises an ultrafine composite metal particle comprising a core made substantially of a metal component and a covering layer made of an organic substance chemically bonded to the core.
For manufacturing ultrafine particles made at least partly of a metal, there has been proposed a process of evaporating the metal in a vacuum in the presence of a small amount of a gas to agglomerate ultrafine particles made of only the metal from the gas phase, producing ultrafine metal particles. Such a physical process, however, does not lend itself to mass production as the amount of generated ultrafine metal particles is small, and is costly because a device for generating an electron beam, a plasma, or a laser beam, etc. or a device for performing inductive heating is necessary to evaporate the metal. In addition, since the particle diameters range in a wide distribution, some of the metal particles remain unmelted when heated, failing to obtain a uniform metal film of low resistance.
When ultrafine particles made of only the metal is used, the ultrafine particles tend to agglomerate in a dispersed liquid, the ultrafine particle dispersed liquid is liable to provide an irregular covering layer. One solution would be to add a suitable surface active agent to the ultrafine particle dispersed liquid to turn them into a protective colloid. However, such a protective colloid fails to provide sufficient dispersion stability.
The bonded structure of ultrafine composite metal particles according to the present invention appears to be such that a core made of a metal component and an organic compound making up a covering layer share metal molecules, or an organic compound and a core form a complex-analogous structure by way of an ionic bond, through the details of the bonded structure are not clear. Since such ultrafine composite metal particles can be produced by a chemical process in a liquid phase, they can be mass-produced at a reduced cost in an ordinary atmospheric environment with a simple apparatus without the need for a large vacuum device. Since the ultrafine composite metal particles have a uniform diameter, all the ultrafine composite metal particles are fused together at a constant temperature. Inasmuch as the ultrafine composite metal particles are covered with an organic metal compound therearound, their ability to agglomerate in a solvent is small, and hence they can easily be scattered uniformly over the surface of the substrate. The ultrafine composite metal particles are stable and hence can easily be handled. Even after the solvent is evaporated, the ultrafine composite metal particles remain chemically stable until they are decomposed with heat and can be handled for easy process management.
According to a method described in claim 4, in the claim according to any one of claims 1 through 3, the ultrafine particles have an average diameter ranging from 1 to 20 nm.
It is known that the melting point of a metal particle is lowered as the diameter thereof is reduced. This effect starts to manifest itself when the diameter of the metal particle is 20 nm or less, and becomes distinctive when the diameter of the metal particle is 10 nm or less. Therefore, the average diameter of the ultrafine particles are preferably in the range from 1 to 20 nm, and preferably in the range from 1 to 10 nm depending on the shape and dimensions of the fine recesses and the structure of the semiconductor device.
According to a method described in claim 5, in the method according to any one of claims 1 through 4, the ultrafine particle dispersed liquid has a predetermined surface tension to increase adhesiveness of the ultrafine particle dispersed liquid to the fine recesses of the substrate and/or areas surrounding the fine recesses.
With the ultrafine particle dispersed liquid having a predetermined surface tension, the applicability of the ultrafine particle dispersed liquid in the fine recesses of the substrate and on areas surrounding the fine recesses is increased. Thus, the substrate with a large amount of liquid held thereon can be dried, so that a sufficient amount of ultrafine particles can be supplied to the recesses and the areas surrounding the fine recesses. Consequently, it is not necessary to repeat the applying and drying steps, and the fine recesses can be filled with the metal according to a simple process.
According to an invention described in claim 6, in the method according to any one of claims 1 through 5, the step of heating the ultrafine particles is carried out under the control of an atmosphere. With this arrangement, an oil mist produced when the ultrafine particles are decomposed is removed from the substrate surface by a nitrogen gas, for example. Therefore, the oil mist is prevented from fuming and becoming stagnant on the substrate surface to contaminate the substrate.
According to an invention described in claim 7, in the method according to claim 6, the step of heating the substrate is carried out in an inactive gas atmosphere containing a small amount of oxygen or ozone, and thereafter in a pure inactive gas atmosphere. The oxygen or ozone acts as a catalyst to separate the organic substance and the metal from each other, thus promoting the decomposition of the ultrafine particles. For example, when interconnections are to be formed using ultrafine particles of silver, the ultrafine composite metal particle layer is heated (baked) while a nitrogen gas containing a small amount of oxygen or ozone is flowing, and thereafter a nitrogen gas containing hydrogen is supplied to reduce the silver to form interconnections of pure copper, after which the gas is changed to a nitrogen gas. In this manner, the interconnections can be formed efficiently.
According to an aspect of the invention, the step of heating the substrate is carried out at a temperature of 450xc2x0 C. or lower. In this manner, any thermal effect on the semiconductor substrate and circuits formed thereon can be reduced.
According to another aspect of the invention, there is provided a method of fabricating a semiconductor wafer by forming an interconnection on a surface of a substrate.
According to a further aspect of the invention, there is provided an apparatus for forming an interconnection, comprising a dispersed liquid supply device for supplying an ultrafine particle dispersed liquid produced by dispersing ultrafine particles made at least partly of a metal in a predetermined solvent, to a surface of a substrate having fine recesses formed therein; and a heat-treating device for heating the substrate to melt and bond the metal.
According to still another aspect of the invention, the apparatus further comprises a polishing device for chemical mechanical polishing the surface of the substrate to remove an excessively attached metal therefrom.
According to still a further aspect of the invention, the dispersed liquid supply device also evaporates the solvent in the ultrafine particle dispersed liquid supplied to the surface of the substrate.
According to yet another aspect of the invention, the apparatus further comprises a supplementary drying device for supplementarily drying the solvent in the ultrafine particle dispersed liquid supplied to the surface of the substrate. With this arrangement, it is possible to completely dry up an organic solvent which cannot be fully dried up by a spin drying process (air drying process) using a spin coater or the like, thus preventing voids from being produced in a heating process.
According to yet a further aspect of the invention, the heat-treating device is arranged to heat the substrate under the control of an atmosphere.
According to another option of the invention, the heat-treating device has a heating plate which houses a heater for heating the substrate at a temperature of 450xc2x0 C. or lower and a cooling mechanism.
According to a further option of the invention, the respective devices are sequentially arranged in an indoor facility along a direction in which the substrate moves. With this arrangement, corresponding steps can successively be performed by the devices in the sequence.
According to yet another option of the invention, the respective devices are accommodated individually in respective chambers disposed radially around a central transfer chamber with a transfer robot disposed therein. With this arrangement, corresponding steps can be individually performed and can be combined with each other.
According to yet a further option of the invention, each of the ultrafine particles comprises an ultrafine composite metal particle comprising a core made substantially of a metal component and a covering layer made of an organic substance chemically bonded to the core.
According to still another option of the invention, the ultrafine particles have an average diameter ranging from 1 to 20 nm.
According to still a further option of the invention, there is provided a dispersed liquid supply device for supplying an ultrafine particle dispersed liquid produced by dispersing ultrafine particles made at least partly of a metal in a predetermined solvent, to a surface of a substrate, comprising: a substrate holder for holding and rotating the substrate; a dispersed liquid supply nozzle for dropping the ultrafine particle dispersed liquid to the surface of the substrate held by the substrate holder at a central portion thereof or an area surrounding the central portion; a bevel washing nozzle for supplying a washing liquid to a bevel of the substrate held by the substrate holder; and a reverse side washing nozzle for supplying a gas or a washing liquid to the reverse side of the substrate held by the substrate holder.
While the substrate is being rotated, the ultrafine particle dispersed liquid is dropped onto the center of the surface of the substrate to uniformly coat the surface of the substrate with the ultrafine particle dispersed liquid. At the same time, the bevel washing nozzle supplies the washing liquid to the bevel of the substrate to prevent the ultrafine particle dispersed liquid from dropping from the edge of the substrate and flowing across the edge of the substrate to the reverse side of the substrate. The reverse side washing nozzles also supplies the gas or the washing liquid to the reverse side of the substrate to prevent the reverse side of the substrate from being contaminated.
According to another alternative of the present invention, there is provided a heat-treating device for heating ultrafine particles made at least partly of a metal to melt and bond the metal, comprising a heating plate for holding and heating the substrate, and a housing having a gas supply port and a gas discharge port and surrounding a space above the substrate held by the heating plate to form a gas chamber between the housing and the heating plate.
By supplying a predetermined gas into and discharging same from the gas chamber defined between the heating plate and the housing, the ultrafine particles are heated under the control of an atmosphere so that an oil mist produced when the ultrafine particles are decomposed is removed from the substrate surface, and prevented from fuming and becoming stagnant on the substrate surface to contaminate the substrate.